In anonymous credential systems, a user with an anonymous credential may prove select private information while protecting other parts of the user's identity. For example, a person may choose to disclose only having a valid driver's license without disclosing name, age, address, etc. (or vice versa).
In some cases, anonymous credentials may be delegated. With delegatable credentials, a chain of delegation may describe a number of users delegating authority in a particular direction.
Some applications of anonymous credential systems include direct anonymous attestation and anonymous electronic identity tokens. Some of these approaches have been captured in implementations including U-prove, Idemix, and java cards.
Anonymous credential systems may include revocation functionality. With revocation, credentials may be invalided. Revocation is useful with regard to many organizational matters, including disputes, compromise, mistakes, identity change, hacking and other insecurities.
Revocation is challenging in anonymous credential systems because it is difficult to anonymously prove that a credential is not revoked. In the case of delegatable credentials, chains of delegation may be difficult to trail because of anonymity protections. As such, revocation may be especially challenging for anonymous credential systems with delegatable credentials.